328 SOILS : PBOPEBTIJES AND MANAGEMENT 



process, there would soon be no mineral food available 

 to plants, as drainage water and the growth of crops take 

 up relatively large quantities of these substances each 

 year ; but in spite of this loss the soil is able to provide 

 at least some plant-food material for each crop, when 

 called upon by the plant. 



229. Solubility of the soil in various solvents. — For 

 purposes of analyses that are intended to show the amounts 

 of mineral plant-food materials in a soil, any one of sev- 

 eral different solvents may be used. These solvents differ 

 in strength, and consequently the percentages of the 

 various constituents obtained from samples of the same 

 soil are different for each solvent. A chemical analysis 

 of a soil is a determination of the quantities of the con- 

 stituents that have been dissolved in the solvent used. 

 Therefore it will readily be seen that the interpretation 

 of a chemical analysis must depend largely on the nature 

 of the solvent, and, unless the solvent is equivalent in 

 its action to some process or processes in nature, the results 

 must be entirely arbitrary. 



The methods that have been used for obtaining solu- 

 tions of the soil for analysis may be grouped as follows : — 



1. Complete solution of the soil 



2. Partial solution with strong acids. 



3. Partial solution with weak acids- 



4. Extraction with water. 



230. Complete solution of the soil. — By the use of 

 hydrofluoric and sulfuric acids and by fusion with alkalies, 

 the entire soil mass may be decomposed and all its inor- 

 ganic constituents determined.^ Such an analysis shows 



^ Wiley, Harvey W. Principles and Practices of Agri- 

 cultural Chemical Analysis, Vol, 1, pp. 398-399. 1906. 



